Effect of Supine Exercise on Left Ventricular Volume and Oxygen Consumption in Man

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Abstract
Twenty subjects with nearly normal left ventricles have been studied during rest and supine leg exercise, by left heart catheterization and use of aortic thermodilution techniques. It was demonstrated that the average end-diastolic volume for the group did not change during exercise, but that the ventricle emptied more completely to a smaller end-systolic volume and accomplished this in less time per beat than at rest. The group could arbitrarily be subdivided into 5 subjects with significantly increased end-diastolic volume, 7 with no significant change, and 8 with reduction in end-diastolic volume. Stroke volume was increased most frequently in the group with increased end-diastolic volume. It is suggested that the response to supine exercise involves primarily increase in rate coupled with an inotropic stimulation of the heart, but that in some instances the Starling mechanism plays a distinct and important part by augmenting ventricular filling and emptying. Energy consumption of the exercising heart could be correlated with those indices reflecting an increase in kinetics of fiber shortening rather than force or tension development, which changed little in these experiments. The increase in external mechanical efficiency during exercise would seem to be due to reduction in mean systolic heart size (with increase in ratio of external to total work of fiber), and to the fact that heart has a basal O2 cost (which becomes a progressively smaller fraction of the total).